In circuit-switched (CS) telephony, a set-up of a call between parties comprises a number of steps. A call is initiated by a first party A, who dials on his A-terminal a telephone number of a B-terminal of second party B. Then, the telephony network routes the call to the B-terminal by using the information of the dialed telephone number. Next, the call is announced to party B by a signal generated on the B-terminal. Then, the B-party can answer the call by some interaction with the B-terminal. The B-terminal signals the network that the call is accepted. After the answer generated by the B-terminal, the call is connected between the A-terminal and the B-terminal and a speech communication between parties A and B is established.
This set-up of a call is implemented in both the wired and the mobile network. Both the A-terminal and B-terminal may be a wired or mobile telephone.
From the prior art a specification for mobile CS-telephony is known (GSM TS 04.07 version 7.3.0, chapter 6.2) which describes a sequence of states of a finite state machine of a telephone device during set-up, progress and termination of a call. FIG. 1 shows a part of the CS-call state diagram 1 from the prior art.
The finite state machine of the telephone (B-terminal) can be in a number of various states. Normally, when the telephone is idle and not in communication, the state of the telephone is the “null” state 10.
From the network as an incoming signal a call request by the A-terminal may be received. Due to this signal, the finite state machine changes its state to a “call received” state 20. The finite state machine arrives at the “call received” state 20 through some intermediate state(s) 15. In this state the user (party B) of the B-terminal is notified of the incoming call. Due to a user generated answer, e.g. pressing an “acknowledge” key on the keypad of the B-terminal, the finite state machine changes to an active state 30, in which speech communication between the party A of the A-terminal and the party B of the B-terminal can be executed. The action of a user generated answer to the incoming call is schematically indicated by block A1, connected by a dotted arrow-line to the “call received state” 20.
The finite state machine arrives at the “active” state 30 through an intermediate state 25. At the same time, a CS-call answer signal is returned to the exchange to establish the speech communication phase.
Upon termination of the call, the finite state machine changes to the “null” state 10, possibly through some further intermediate state(s) 35. At this time, termination of the call is indicated to the exchange.
In the prior art, the party B is required to activate the B-terminal by performing some manipulation of the B-terminal, e.g., by pressing some “acknowledge” button on the terminal.
The above mentioned method of answering the incoming call adversely restricts the usability and functionality of the telephone, i.e., the method of the prior art may limit user-directed services.